Do you mow at 540

[geneP]

The quality of cut is somewhat dependent on the tip speed of the blades. The tip speed is affected by the PTO rpm, the gearbox ratio, and the length of the blades. It seems as if there is no "standard" gearbox ratio, but most of the ones I've tried to measure are around 1.5 rpm of the output shaft to 1 round of the input (PTO). A 6' mower will have more tip speed than a 4' or 5' with the same ratio gearbox. I bought an off-brand 6' brush hog mower that makes the blades whistle. Unscientific measureing makes me believe it's more like 1.9 ratio. I can gear my tractor up one gear and reduce the engine rpms about 300-400 and still get a clean cut. I've said all that to say that quality of cut are dependent on much more than pto rpm.

 

[have_blue]

I happen to catch the highlights of your post Bob and the way that I 1st interpreted it thought that you were touching up your blades with paint after each mowing. Thought to myself, "Man wish I had that kind of diligence." Then the true subject matter of what you were saying hit me. Boy did I feel foolish!

Uhhh... ya, PR, I use epoxy-based paint between mowings to prevent rust. Ya, right!

All seriousness aside, for brush, follow sharpening directions. For grass and light weeds, very sharp blades get excellent results. The object of the game when cutting grass and light weeds is to use the lowest RPM that yields a clean cut. The duller the blades, the higher that number will be, up to the attachment's recommended maximum.

 

[Birdman253]

PTO implements are designed to operate at greatest efficiency at rated PTO speed, i.e. 540 rpm, or 1000 rpm for (very high horsepower applications). If the operator's manual states to run at 540, then defer to the design engineers that designed the machine. In the long run, you will get greater efficiency, and often less wear on the unit.

I hear many of you asking how will I get less wear running 540 than if I run at 450. A good example of this is inside your gearbox of a mower. When running at rated speed on the PTO, you have the proper blade tip speed. This translates into kinetic energy that helps to "drive" the edge through the material being cut. If you slow down the machine, you now get slower speeds, less force, and have higher torque loads on the entire drivetrain, from the flywheel of the engine all the way to the tip of the blade.

With all this said, there are certain, very limited instances when the PTO speed should be reduced. A good example of this is a round baler, when baling very dry, short hay. Often under these conditions, the rotation of the bale causes material to "flake" off, and either drop out of the machine, or accumulate in all areas of the unit. Under these conditions, it is proper to slow the PTO to correct the problem. But guess what, in the operator's manual it describes this condition, and instructs you to slow the PTO.

If you always follow the owner's manual, you will be much better off in the long run.

 

[Soundguy]

'RTFM' is actually very good advice. However.. it seems many people are perfectly willing to plunk 10-20-30 thousand dollars down on a machine and not even get a manual.. ( or read it ).

I make that a priority when i get a new tractor.. that is.. get the owners/operators manual, -at least-.. and if possible a shop or service manual/ parts manual, if available.

Same with implements. Who wants to run a High dollar mower.. but not pay the 80$ for the manual ( in the case where the manual is not included.. or -lost- by the dealer.. etc. )

Soundguy

 

[Farmwithjunk]

Every tractor model and/or brand is different. But in general, the RPM where 540 RPM PTO speed is achieved is USUALLY not where peak HP is achieved. Sometimes it's quite a bit different. On one of my tractors, 540 rpm's on the pto is at 1700 engine rpm. Peak HP is at 2250 engine rpm. At pto speed, hp level is (according to some old specs I have) 15% less than peak HP. That isn't uncommon. Most farm tractors I've been around will have the 540 rpm pto speed marked in some manner on the tach. Also, you'll find a "do not exceed" mark for pto use that's a tad faster and closer to peak engine hp output.

In the end, this isn't rocket science. So long as the engine pulls the mower (or whatever pto load is) and it cuts like you'd expect, it isn't all that critical what rpm you run at. However, in about every case I've seen, mower performance, as well as engine performance is better when you operate at or near manufacturers suggested levels. There are exceptions to every rule. In tough conditions, I'll run at or near that peak rpm level.

It's always been my thinking that the people that designed and built my equipment may just know more about the subject than I. When they give me a suggestion on how to operate it, I listen. Until someone or something proves that wrong, I'll stick with what got me here.

 

[scott_vt]

540 RPM PTO speed is like 2600 Tach. RPMs on our TC-40D. However I tend to run the RFM at about 2K RPM with good results.

I don't mow wet grass though.

HOH,
Im with Mike on this one, 2000 RPM on my Massey is about 450 PTO RPM and it works fine for me, Ill occasionally bog down on a steep hill in real thick grasses but usually only a couple hundred RPM.

Mower cuts great at that speed

 

[HEC]

The 540 speed is at 2500 on the tractor I have now and I very seldom ever go that high.I have a 6ft bush hog on a 50 plus pto hp tractor so I really don't have ton all the tractors I have had I listen to the engine and make sure it isn't lugging and run anywhere from 1700 on up when bush hogging , depending on what I am cutting and what gear I am running in.If you are having trouble with heavy grass bunching up you maybe trying to cut a little to close and not giving the cut grass a way to escape , try lifting your bush hog a little higher and it should solve that problem.

 

[have_blue]

I hear many of you asking how will I get less wear running 540 than if I run at 450.

I don't think 540 RPM is a magic number. I think it's a very general guideline. I think you must adjust accordingly instead of blindly running at a particular speed. I think the 540 RPM spec was a compromise reached by implement and tractor makers many years ago, and not much more. Modern metallurgy and design changes the whole equation. I think it's almost impossible to under work a tractor or implement. I bet you that not many implements and tractors are brought to the dealer for repairs for being under worked.


Here's proof for me: Running my tractor and my brush hog at 540, there is a lot of stuff going on under the deck. The grass is being cut, re-cut, shredded, and big balls of grass are left in my wake. My tractror is straining a little bit, and fuel usage is high. My cutter's gearbox gets quite hot. At 425, there is little noise, banging, or vibration. The blades make a nice swishing noise as they cut. Grass and weeds come out mostly whole, and lay down evenly. Fuel usage is excellent. My gearbox is very warm, but not hot. My gearbox is rated for 55hp, my PTO hp is 30. All the signs point to 425 being more efficient than 540. I don't think I'm in any danger of under working anything! YMMV, of course!

 

[TrippleT]

I have blue too, and I run my Maschio 72 in rear discharge finish mower around 2000 to 2100 RPM on the tach. I tried running around 2400, or until the 540 light came on, and the gear box got hot enough to force gear oil out of the vent.
Bottom line is that I run lower speeds and get just as good results. I have doubts about the accuracy of the lights, or even the tach. But I have had just as good results running slower. I think that everyone has to get familiar with their equipment and the job at hand. Do a little experimenting and what works best is usually best.

 

[Propertymaint]

Just another opinion here, I rarely run at 540 pto rpm. I typically run enough throttle to keep the engine from lugging and produce decent results from whatever attachment I am using whether it is a mower, chipper, loader or backhoe. When finish mowing I typically run about 2200 rpm on the engine and a ground speed which is comfortable for both tractor and operator, I don't notice any difference in cut quality If I run up to 2600 rpm (or 540 PTO speed) but I will notice that the engine sounds like it is screaming and that fuel consumption is considerably greater running at the higher rpm especially after a full day of commercial mowing. I don't buy the 540 PTO rule or the other rule I have heard about having to run a hydro tractor at full throttle. I agree an engine needs to run at a comfortable rpm to prevent lugging and an attachment needs to operate at a certain rpm to produce good results but I feel - and this is just my opinion -that a little common sense and good old fashion listening to your tractor will dictate what rpm you should be operating at. I guess I'll let you know if my stubborn line of thinking causes any premature failures.